The invention concerns an electrical transmission line with at least one distributed low-pass filter to suppress high-frequency spurious signals (noise) present on the line.
Known noise protection filters with discrete circuit elements, which can be ohmic, capacitive and inductive, as one chooses, have a drawback in that the parasitic inductances connected to their capacitive circuit elements, or the parasitic capacitances connected to their inductive circuit elements, give rise to undesirable resonances in the region of high frequencies.
Shielded electrical lines with at least one distributed low-pass filter used as noise protection filters are known from the journal IEEE Transactions on Electromagnetic Compatibility, January 1964, pages 55 to 61, and from the journal Proceedings of the IEEE, January 1979, pages 159 to 163, and from West German Patent No. 29 39 616. In the first-cited literature source, a coaxial transmission line is described which has one or several line sections with a magnetic material, such as a ferrite material, between the central conductor and the external shielding as lossy insulation material. A similar coaxial noise protection filter, equipped with a magnetic ceramic material, essentially proposed as a feed-through filter, is described in the second-named literature source. In German Patent No. 29 39 616 a lossy electrical cable is described in which at least one conducting element is used in connection with an absorbing mixture at least partially surrounding the conductor and having a composite construction, namely a core formed of a filament or a fiber and a conductive coating of the type such that the element exhibits high resistance with good mechanical properties.
The known distributed low-pass or noise protection filters exhibit drawbacks in that they must exhibit high magnetic losses, dielectric losses or conductive losses in the insulation material, since only such high losses produce the desired low-pass effect, and that they have a sophisticated design that hampers not only their manufacture but also their universal applicability.